Once upon a time there was a president, wavering in popularity. He was deemed by some political pundits as “highly beatable.” He had just done his whole thing with health care, which left voters fuming, and two years before the presidential election, Republicans picked up a slew of seats in the House, taking control. But then, the Republican Party did the unthinkable: It gave the nomination to a guy because it was essentially “his turn,” and the candidate got shellacked by the incumbent Democratic president. That president was Bill Clinton; the “It’s His Turn” candidate was Bob Dole; the year,...